Process of bleaching clay



messes m geese-.595

Paten tecljan. 1s, 144

PROCESS ()FELEACHING CLAY Ira Williams, Borger, Tex., and Nathan Millman, Macon, Ga., assignors to Sgoda Corporation, Huber, Ga., a corporation of New Jersey No Drawing. Application August 5, 1941, Serial No. 405,564

19 Claims.

This invention relates to the bleaching of clay and more particularly to an improved process of bleaching clay with salts of hydrosulfurous acid.

It is known that the whiteness of clay can be improved by various bleaching processes. The most common bleaching agents, employed in the bleaching of clay, have been hydrosulfites, either added as such or formed in situ in the clay slip. For example, it has been proposed to bleach clay by adding to a clay slip a hydrosulfite, such as sodium and zinc hydrosulfites, whereby a relatively large concentration of bleaching agent is immediately available. It has been considered necessary to carry out the bleaching with such agents in the presence of a strong acid in order to produce a satisfactory bleaching action. In other cases, it has been proposed to form hydrosulfites in situ in the clay slip by adding zinc and sulfur dioxide or zinc and sodium bisulfite in the presence of a strong acid, whereby the zinc is supposed to react with the sulfur dioxide or the sodium bisulfite to produce a slow evolution of hydrosulfite in low concentration. It has also been proposed to bleach clay slips with sodium formaldehyde sulfoxylate and the like. In the presence of the strong acids, such bleachin agents tend to produce objectionable amounts of sulfur dioxide fumes. Also, in some cases, the acidity noticeably affects the general properties of the resulting clay frequently in an undesirable manner.

It is an object of our invention to provide an improved process for the bleaching of clay, whereby a large improvement in the color of the clay is obtained. Another object is to provide a process for bleaching clay slips which avoids the generation of objectionable amounts of sulfur dioxide fumes. A further object is to provide a process of bleaching clay slips, whereby the slips can be bleached under either acid, neutral or alkaline conditions. to provide an improved method of bleaching clay with a metal salt of hydrosulfurous acid. Other objects are to advance the art. Still other objects will appear hereinafter.

The above and other objects of our invention may be accomplished by treating a clay slip with a preformed water-soluble metal salt of a hydrosulfurous acid in the presence of powdered zinc in an amount equal to at least 25% of the weight of the salt. We have found that, by bleaching clay by such process, we are able to bleach the slip under either acid, neutral or alkaline conditions without the production of objectionable A still further object isamounts of sulfur dioxide fumes and at the same time obtain a clay of greatly improved color.

By a preformed metal salt of hydrosulfurous acid, we mean one which is completely formed prior to its addition to the slip, as distinguished from one formed in situ in the slip by reaction of the ingredients necessary to form the salt in the slip. We have found that the salts, formed in situ in the slip, are not equivalent to the preformed salts and will not produce the same results. Also, by salts, we mean the simple salts and do not intend to include the complex compounds, such as the sulfoxylates, formed from aldehydes, ketones and the like.

Any Water-soluble salt of hydrosulfurous acid may be employed in the process of our invention. Suitable salts, which have proved to be particularly satisfactory for our purpose, are sodium hydrosulfite, zinc hydrosulfite and calcium hydrosulfite. "We particularly prefer to employ sodium hydrosulfite. The amount of the hydrosulfite employed may be widely varied and will be largely dependent upon the operator and the degree of bleaching desired. Generally, the amount of hydrosulfite employed will besmall, usually on the order from about 2 to about 6 pounds per ton of clay.

The amount of powdered zinc employed with the hydrosulfite may be varied widely. As little as 25% of zinc, based on the weight of the hydrosulfite, has proved to be effective. From about 25% to about 200% of zinc, based on the weight of the hydrosulfite, will generally be found to be satisfactory. Larger amounts of zinc may be employed, if desired, but without advantage. We have employed as much as 400% of zinc, based on the weight of the hydrosuliite. Preferably, we employ the zinc in-the proportion of from about 33% to about of the weight of the hydrosulfite.

As has been indicated above, the clay slips, treated in accordance with our invention, may be either; acidic, neutral or alkaline as desired. The acidic, neutral or alkaline condition of the slip may be maintained throughout the entire bleaching period or the pH of the slip may be altered during the course of the process. Thus, it is possible, through our process,.to alter the workingcharacteristics of the clay to a considerable extent by controlling the pH of the slip during the bleaching process. Preferably, we maintain the pH of the slip between about 3.5 and about 4.5 during the bleaching process. However, it will be understood that, when a clay of different working characteristics is .desired,

we will prefer to operate under neutral or alkaline conditions. When it is desirable to bleach under acid conditions and the slip is not naturally of the desired pH, we may add a suitable acid to produce the desired pH. When an acid is added, it should preferably be a strong non-oxidizing mineral acid, such as sulfuric acid, hydrochloric acid, phosphoric acid and the like, and particularly sulfuric acid.

Our process may be carried out with the clay slip at any desired temperature between the freezing point and the boiling point of the slip, particularly from about C. to about 95 C. However, we have found that the best results are obtained when the clay slip is bleached at a temperature of from about 60 C. to about 80 C.

After the bleaching operation is completed, the clay may be separated from the slip in any convenient manner and dried. Where an acidic clay is unobjectionable, it will usually be convenient to add a small amount of a strong mineral acid, such as the strong non-oxidizing acids, represented by sulfuric acid, hydrochloric acid, and phosphoric acid in order to coagulate the clay and improve its filtering characteristics, as well as to aid in the removal of iron salts and the like. When it is desired to separate alkaline clay from alkaline slips, which generally cause diificulty in filtering, the clay can be deposited electrically or the slip can be treated with coagulants which are efiective to coagulate the clay without producing an acidic slip.

In order to more clearly illustrate our invention, the preferred modes of carrying the same into effect and the advantageous results to be obtained thereby, the following examples are given:

Example 1 A sample of degritted Georgia kaolin was prepared in the form of a slip which contained 44 percent of clay. This slip was divided into three portions which were treated as follows. Portion A was treated with sulfuric acid at the rate of 5 pounds per ton of clay. The clay was filtered off after 2 /2 hours. Portion B was treated with 3 pounds per ton of sodium hydrosulfite and, after standing for 2 /2 hours, 5 pounds per ton of sulfuric acid were added and the slip was filtered immediately. Portion C was treated with 3 pounds per ton of sodium hydrosulfite and 2 pounds per ton of powdered zinc. After standing for 2 hours, 5 pounds per ton of sulfuric acid were added and the slip was filtered immediately. All of the filtered samples were dried at 90 C. The whiteness of each sample was determined with the General Electric reflectance meter with the following results. Control sample A83.i0; sample B84.00; sample C84.27. These results show that a material improvement was produced by the presence of the zinc.

Example 2 This experiment was conducted with a clay slip similar to that used in Example 1. The amounts of the chemicals used were exactly as in Example 1 but the temperature and time of treatment were varied. The slip was heated to 80 C. in each case. Portion A was treated with sulfuric acid and filtered immediately. Portion B was treated with sodium hydrosulfite, held at 80 C. for minutes, treated with sulfuric acid and filtered. Portion C was treated with sodium hydrosulfite and zinc powder, held at 80 C. for 15 minutes, treated with sulfuric acid and filtered. All of the filtered samples were dried at 90 C. The whiteness, as determined with the General Electric reflectance meter, was as follows: Sample A-83.1l; sample B-84.02; samle C--84.22.

Example 3 5 1 l 5 Temp. 1 Time of General bleaching Electric bleach, before addbright- O. ing acid ness Bleaching Lbs/ton Zinc material cl.

Zinc hydrosul- 3 30 2%; hours"! fite. 1 L

2% hours... 15 minutes. 15 minutes 2% hours...

(two/o:

(SON

) 2% hours" 83. 90

l l i l l l i i l Example 4 A clay slip, containing 38% of kaolin, was heated to 80 C. and treated with 5 pounds per ton of sulfuric acid, 2 pounds per ton of sodium hydrosulfite and 1 pound per ton of powdered zinc. The pH of the slip was approximately 2.3. After 30 minutes, the slip was filtered and dried. The brightness was 84.12. A control, which contained the sulfuric acid and sodium hydrosulfite but no zinc, had a color of only 83.84.

Example 5 A 40% slip of kaolin was prepared and divided into four portions to determine the effect of the hydrogen ion concentration on bleaching. One portion was not bleached. The pH of this sample was 5.7. The brightness of this sample was i found to be 82.56. A second portion was bleached at C. for 60 minutes with 2.5 pounds per ton of sodium hydrosulfite and 1.5 pounds per ton of zinc dust. The slip was then coagulated with 5 pounds per ton of sulfuric acid and sodium carbonate was added to produce a pH of 4.8. The color of the resulting clay was 84.95. A third portion was treated with 3 pounds per ton of sodium carbonate to produce a pH of 8.95. It was then bleached for 60 minutes at 60 C.

". with 2.5 pounds of sodium hydrosulfite and 1.5

pounds of powdered Zinc per ton of clay. The slip was then coagulated by adding sulfuric acid until the pH of the slip was 4.75 and the slip was filtered. The color of the clay was 84.56. A fourth portion was treated exactly as the third portion exceptthat no acid was added and the final pH of the slip was 7.75. The slip wa filtered and the resulting clay had a brightness of 83.97.

These results were particularly surprising since previous attempts to bleach clays with hydrosulfites under alkaline conditions have resulted in the production of clay which i grey, with little or no improvement in brightness.

Example 6 The results, obtained by the practice of our invention, cannot be obtained by forming the salt of hydrosulfurous acid in situ in the clayslip even in the presence of substantial amounts s. BLEACHlNG t creme; Hum

REAT'MENT 8L EIAHON OF TEXTlLES 6t HBERS,

CHEitllCAL MOBXFL of excesszincfi A portion .of a'clay slipwas bleached,- in, accordanc with the process described by A. H. Bumpin his Patent 2,149,506, employing amounts of ingredients as follows:

Clay 200.

Zn n .1 I .3 ZnSzO4 .0163 gram mole Zn .15

Clay 200.

Sodium hydrosulfite 284 =.0163 gram mole Zn .15

The bleaching continued for 2 hours and then the clay was filtered off and dried. The resulting clay had a brightness of 83.7.

It will be understood that the above examples are given for illustrative purposes only and that our invention is not tobe limited to the specific embodiments disclosed therein, but we intend to claim our invention broadly as in the appended claims. Many variations and modifica tions of our process will be readily apparent to those skilled in the art, which modifications and variations will fall within the scope of our invention. For example, the proportions of ingredients, the temperatures, the pH of the slips and the method of operating the process may be widely varied within the limits hereinhefore set forth. Also, other supplementary treatments, known to the art, may be employed when, as and if desired. For example, in some cases ferrous iron compounds remain in the slip as simple water-soluble salts, which have a tendency to re main with the clay, if not thoroughly washed out, and will oxidize to colored ferric salts and thus produce a yellow clay. In such case, the iron compounds may be converted into th form of blue or slightly colored stable salts according to the methods well known to the art in order to prevent the iron compounds from reverting to yellow or brown colored compounds during the drying of the clay. Still other variations and modifications will be apparent to those skilled in the art.

We claim:

1. The process of bleaching clay which comprises adding to a clay slip a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to at least 25% of the weight of the salt.

2. The process of bleaching clay which comprises adding to a clay slip a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to from about 25% to about 200% of the weight of the salt.

3. The process of bleaching clay which com- I and .powderedi zin'c in an amount equal teat-least 25% of the weight ofthe'salt; a 5."Ihe process of bleaching clay which comprises adding to a clay slip at about 60 C. to about as small proportion of a preformed water-soluble metal salt of hydrosulfurou acid and powdered zinc in an amount equal to from about 33% to about of the weight of the salt.

6. The process of bleaching clay which comprises adding to aclay slip a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to at least 25% of the weight of the salt, in the absence of added strong mineral acid, then, when the bleaching is completed, adding a. small proportion of a strong mineral acid to coagulate the slip and then filtering out the bleached clay.

'7. The process of bleaching clay which comprises adding'to a clay slip a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to from about 33% to about 00% of the weight of the salt, in the absence of added strong mineral acid, then, when the bleaching is completed, adding a small proportion of a strong mineral acid to coagulate the slip and then filtering out the bleached clay.

8. The process of bleaching clay which comprises adding to a clay slip at about 60 C. to about 80 C. a small proportion of a preformed watersoluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to from about 33% to about 100% of the weight of the salt, in the absence of added strong mineral acid, then, when the bleaching is completed. adding a small proportion of a strong mineral acid to coagulate the slip and then filtering out the bleached clay.

9. The process of bleaching clay which comprises adding to an alkaline clay slip a small proportion of a preformed Water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to at least 25% of the weight of the salt.

10. The process of bleaching clay which comprises adding to an alkaline clay slip a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to from about 33% to about 100% of the weight of the salt.

11. The process of bleaching clay which comprises adding to an alkaline clay slip at about 60 C. to about 80 C. a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to from about 33% to about 100% of the Weight of the salt.

12. The process of bleaching clay which comprises adding to an alkaline clay slip a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to at least 25% of the weight of the salt. then, when the bleaching is completed, coagulating the slip and filtering out the bleached clay.

13. The process of bleaching clay which comprises adding to an alkaline clay slip at about 60 C. to about 80 C. a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to from about 33% to about 100% of the weightof the salt, then, when the bleaching is completed, coagulating the slip and filtering out the bleached clay.

14. The process of bleaching clay which comvul u" l IUUI ll prises adding to an alkaline clay slip a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to at least 25% of the weight of the salt, then, when the bleaching is completed, adjusting the pH of the slip to between about 4.75 to about 7.75 and filtering out the bleached clay.

15. The process of bleaching clay which comprises adding to an alkaline clay slip at about 60 C. to about 80 C. a small proportion of a preformed water-soluble metal salt of hydrosulfurous acid and powdered zinc in an amount equal to from-about 33% to about 100% of the weight of the salt, then, when the b1eaching is completed, adjusting the pH of the slip to between about 475 to about 7.75 and filtering out the bleached clay.

16. The process of bleaching clay which comprises adding to a clay slip a small proportion of preformed sodium hydrosulfite and powdered zinc in an amount equal to at least 25% of the weight of the salt.

" amount equal to from about 33% to about 100% of the Weight of the sodium hydrosulfite.

19. The process of bleaching clay which comprises adding to a clay slip at about 60 C. to about 80 C. a small proportion of preformed s0- dium hydrosulfite and powdered zinc in an amount equal to from about 33% to about 100% of the weight of the sodium hydrosulfite, in the absence of added strong mineral acid, then, when the bleaching is completed, adding a small proportion of a strong mineral acid to coagulate the slip and then filtering out the bleached clay.

IRA WILLIAMS.

NATHAN MILLMAN. 

